The invention relates to a holder for flat subjects, in particular semiconductor wafers, according to the introductory part of claim 1.
In the last years the continuously increasing miniaturization of semiconductor element structures causes more stringent and new demands on the manufacturing process of electronic components. Thus with the lithography procedure with structure sizes below 0.5 .mu.m the surface of the semiconductor material to be exposed must be very planar (profile difference &lt;0.4 .mu.) in order to lie within the focussing plane. For this the material must be planarized by way of a suitable device.
From DE 195 44 328 or from the company document "CMP Cluster Tool System Planarization Chemical Mechanical Polishing" of Peter Wolters of March 1996 it is known to provide polishing and cleaning stations for wafers. After polishing, the wafers run through a cleaning station, wherein from the later document it is known to arrange the polishing and cleaning station in a pure space and to separate these from a space from which the semiconductor wafers exit and are put into the pure space from which they exit, with the help of a suitable transfer device. The wafers are held in processing units by holders and are pressed by these holders against the polishing working surfaces. The holders or holding heads are connected to a spindle of a drive machine; the position of the spindle is mounted in a height adjustable manner in order to press the wafers against the working surfaces. In order to obtain an adequate planarity the lower holding plate which holds the wafer via vacuum channels or vacuum bores, is linked via a universal joint onto a carrier section which for its part is connected to the spindle of the drive device. The pressing force is applied exclusively via the universal joint to the holding plate and thus to the wafer. This leads to a relatively high loading of the joint and brings with it the danger that the pressing pressure is not uniformly distributed.